The invention relates to a hybrid inflator comprising a combustion chamber and a pressure gas tank, wherein in the idle state of the hybrid inflator a discharge opening of the pressure gas tank is closed by a bursting element which can be destroyed by means of a penetration element in the case of function of the hybrid inflator. In addition, the invention relates to a method of operating a hybrid inflator, to an airbag module and to a vehicle safety system.
Occupant restraint systems for automotive vehicles usually include airbag modules comprising an airbag which in the case of crash is inflated so as to reduce the probability of collision of body parts of a vehicle occupant with a vehicle component. For inflating the airbag in the case of crash, for example hybrid inflators are provided which consist of a pressure gas tank comprising compressed gas or cold gas in the idle state of the hybrid inflator and a pyrotechnical subassembly, wherein the pyrotechnical subassembly serves for triggering and/or heating the gas that is originally compressed and is discharged in the case of function of the hybrid inflator. The pressure gas of such hybrid inflator may be closed toward the pyrotechnical subassembly in a pressure-tight manner.
This is enabled, for example, by a bursting membrane and, resp., by a bursting cap to which in the idle state of the hybrid inflator pressure gas stored in the pressure gas tank can be or is applied on its outer peripheral side. By the term “in the idle state” and, resp., “in the idle state of the hybrid inflator” it is to be understood that the hybrid inflator has not yet been activated or, in other words, relating to the bursting membrane, that the bursting membrane is closed and no activating signal is yet provided in response to which the bursting membrane is to be opened or burst.
Document EP 1 053 915 B1, especially FIGS. 1 to 4 there, illustrate the structure of a hybrid inflator comprising a storage chamber as well as a pyrotechnical ignition device. The storage chamber is separated from a combustion chamber with the aid of an inner cap or an inner membrane. In the case of activation or function of the hybrid inflator, the inner cap or the inner membrane is ripped and, resp., opened by a piston-like device. For this, a movably supported piston and a guiding device are provided, wherein the piston is pressurized in the case of activation so that the piston pierces the inner cap or the inner membrane. For guiding the piston part carriers as well as guide means are required. This is a relatively complex design consisting of plural components and seals which have to be provided, inter alia, with expensive component tolerances.
Moreover, it has turned out that a piston as shown in EP 1 053 915 B1 can temporarily close the discharge opening of a pressure gas tank again after activation of the hybrid inflator so that no continuous discharge of the gas present in the pressure gas tank can be guaranteed.
Further, it is known that for igniting a pyrotechnical propellant in airbag inflators openings of a combustion chamber in which such propellant is received are closed by tamping on the inside of the combustion chamber so as to obtain uniform ignition of the entire propellant and/or particular pressure build-up inside the combustion chamber before the openings of the combustion chamber are released by bursting of the tamping. Said tamping then ruptures at a predetermined increased pressure in the combustion chamber. Said pressure is dependent on the strength and the thickness of the tamping as well as on the diameter of the openings. Frequently the opening pressure of the tamping is similar to the maximum combustion chamber pressure. The relatively high opening pressure results in a sudden discharge of gases. This is also known by the term “high onset” requiring extremely high strengths of the module casing and of the airbag.
For the mechanical opening of the pressure gas tank the bursting element thereof is destroyed according to EP 1 053 915 B1 by a piston. Previous hybrid inflators exploit the pressure inside the combustion chamber generated by the pyrotechnical combustion for moving the mechanism. Said pressure prevailing in the combustion chamber is higher than the internal pressure of the pressure tank for sufficiently safe opening of the pressure tank. Such required high pressure inside the pyrotechnical combustion chamber requires sufficiently high strength in the combustion chamber design. As soon as the functional pressure of the combustion chamber is designed to be higher than the filling pressure of the pressure gas tank, the combustion chamber has to be designed to exhibit an appropriately high strength.